The present invention relates to a molding material for OA machine parts with improved vibration-damping properties, particularly it relates to such a molding material comprising a polyphenylene ether-based or polycarbonate-based resin having high mechanical strength, heat resistance and dimensional accuracy.
Since polyphenylene ether-based resins and polycarbonate-based resins have many excellent properties such as high mechanical strength, heat resistance, dimensional stability and flame retardancy, they are popularly used as material of various commercial products in many fields of industry, such as typically electronic parts, electrical apparatus and automobile parts.
Recently, most remarkably, these polyphenylene ether-based and polycarbonate-based resins are used instead of the conventional metals and thermosetting resins, as material of the business machine parts, especially chassis parts of such office machines as copiers and facsimiles, or the chassis parts or trays of the disc drives such as CD-ROM drive, DVD, FDD, HDD, etc., used in personal computers. This owes to the excellent properties such as high mechanical strength, heat resistance, dimensional accuracy and flame retardancy of the polyphenylene ether-based and polycarbonate-based resins. In applications where high rigidity is required, the reinforced polyphenylene ether or polycarbonate resins containing inorganic fillers are used. Development of these resin materials is also answering to the request for smaller size and thickness of the products in recent years.
Lately, however, there has arisen the problem of vibration incidental to the operational speed-up of the OA machines. Vibrations generated at their source, such as motor in a device, are transmitted to the resin-made parts, especially chassis parts, to let them vibrate, which is liable to result in causing blurring of the image or difficulty in reading data. For instance, the increase of processing speed in the case of copying machines or the increase of rotation speed in the case of disc drives such as CD-ROM drive has boosted the generated frequency to a very high level, such as 1,000 Hz in some cases, in contrast with the frequency of up to about 200 Hz in the conventional devices.
Because of such elevation of the output frequency, it has now become difficult to hold down vibrations of the chassis parts, in which it has been possible to overcome by increasing thickness or by proper designing of the rib structure in the conventional products. In the resin material, efforts have been made to increase rigidity by blending a greater amount of inorganic filler to raise the resonance frequency, so that the resonance frequency may be left out of the range of generated frequency. However, there is a limitation due to excessive elevation of the generated frequency. As another antivibration means from the resin material, it is suggested to use a material which is capable of absorbing vibrations. However, such vibration-absorbing materials are poor in rigidity and heat resistance, and impracticable for the OA machine parts.
Further, in a resin molding material for OA machine parts, excellent flame-retardant property is required. Usually, the flame-retardant property is evaluated by UL94 test. In a resin molding material for OA machine parts, the flammability of V-0, V-1 or V-2 rank according to UL94 vertical combustion test is required. However, it is difficult for a resin molding material for OA machine parts to satisfy the excellent vibration damping properties and excellent flame-retardant property, simultaneously.
Under these circumstances, there has been desired development of a resin molding material having improved vibration damping properties and flame-retardant property while maintaining high mechanical strength and heat resistance required for the OA machine parts.
As a result of the present inventors"" earnest studies to solve the above problem, it has been found that a molding material comprising a polyphenylene ether-based or polycarbonate-based resin composition having a specific modulus of elasticity and damping ratio, is suited for the OA machine parts. The present invention has been attained on the basis of the above finding.
An object of the present invention is to provide a molding material for OA machine parts which has excellent vibration damping properties and flame-retardant property, by using a polyphenylene ether-based or polycarbonate-based resin with high mechanical strength, heat resistance and dimensional accuracy.
To attain the above aim, in an aspect of the present invention, there is provided a molding material for OA machine parts comprising a resin composition comprising:
(1) 60 to 98 parts by weight of a polyphenylene ether-based resin comprising 10 to 100% by weight of a polyphenylene ether resin and 0 to 90% by weight of a styrene-based resin, or a polycarbonate-based resin comprising 50 to 100% by weight of a polycarbonate resin and 0 to 50% by weight of a styrene-based resin;
(2) 2 to 40 parts by weight of a thermoplastic elastomer which is a conjugated diene rubber having not less than 50% by weight of 1,2-vinyl structure, 3,4-vinyl structure or mixture thereof, a styrene-conjugated diene block copolymer having not less than 50% by weight of 1,2-vinyl structure, 3i4-vinyl structure or mixture thereof, or a hydrogenated product thereof; and
(3) 1 to 50 parts by weight of a flame retardant,
the total amount of (1) polyphenylene ether-based or polycarbonate-based resin and (2) thermoplastic elastomer being 100 parts by weight,
said resin composition having bending modulus of not less than 1500 MPa as measured at 23xc2x0 C. according to ASTM4 D790, a damping ratio of not less than 1.0% at 23xc2x0 C., and a thermal deformation temperature of not less than 100xc2x0 C. as measured according to ASTM D648 under 18.6 kg/cm2 load,, and
the product of the bending modulus and the damping ratio being not less than 10,000 MPa.%.